The present invention relates to a fastening device for sports shoes, such as for example ski boots or skates.
Several fastening devices for ski boots are currently known: Italian patent no. 821919, filed on Dec. 16, 1967 discloses a tensioning lever for closing ski boots which is characterized by a metal core covered on all sides by plastics that can be applied by injection-molding or by molding.
However, in the effort of reducing manufacturing costs, this solution has shown some drawbacks: the considerable reduction of the metal portion by injecting plastics over it, has undoubtedly weakened the overall structure of the lever, whose portion made of plastics can break and/or warp in case of accidental impacts.
The portion made of plastics is in fact directly affected by impacts because it surrounds the metal portion.
Furthermore, the two components may disengage from each other, consequently causing possible deformation of the lever during closure.
Italian patent no. 843875, filed on Sep. 24, 1968 discloses a fastening lever made of plastics which is characterized in that a profiled metal bar is provided on the upper part of the fastening lever and runs longitudinally along the lever. The bar is rigidly associated with the portion made of plastics of the lever and is arranged so that at least the upper part of the profile is external and visible.
The profiled metal bar is substantially U-shaped and merely serves to strengthen the portion made of plastics; it can be considered equivalent to a longitudinal rib which cannot cooperate effectively with the plastics to increase the strength of the lever due to its small extension and cross-section.
Accordingly, any accidental impact, which usually occurs laterally with respect to the lever, affects only the portion made of plastics, which is accordingly intrinsically subject to breaking.
Italian patent Application no. 41524 A/79, dated Feb. 28, 1979 discloses an improvement in the construction of fastening levers used in ski boots which substantially uses a U-shaped tempered steel blade which is inserted at an adapted channel formed on a portion made of plastics.
This solution, too, has drawbacks: as the two elements are practically both U-shaped and mutually superimposed to obtain the lever, the portion made of plastics may disengage from the metal one due to accidental impacts. On one hand this makes it difficult to activate the lever, and on the other hand the metal portion may break or deform, with the consequent need to replace the entire lever.
When opening the lever, the user also applies a considerable stress to the portion made of plastics, which can disengage from the metal portion.
U.S. Pat. No. 4,951,364 discloses a locking lever for ski boots which is substantially constituted by a metal portion having side walls covered with plastics.
In this solution, however, the functionality of the lever is provided exclusively by the metal portion, whereas the portions made of plastics have a merely aesthetic function, without thus increasing the strength of the lever in any way.
European patent application EP 542339 discloses a closure and engagement lever for ski boots which has a central body made of plastics with lateral portions made of metal. However, even this solution, which is similar to the previously described one, has drawbacks: the metal portion absorbs all lateral impacts and transmits them directly and fully to the portion made of plastics, which may break.
Furthermore, as the lateral metal portions are not directly connected to each other, torsion stress may be produced during the closing or opening of the lever, leading to accidental breakages.